Cabin pressure control



Feb. 4 R. A. FISCHER CABIN PRESSURE CONTROL Filed May 25, 1950 INVENTOR. em /flea H. F/sch'ee Patented Feb. 16, 1954 CABIN PRESSURE CONTROL Richard A. Fischer, Los Angeles, Calif., assignor to The Garrett Corporation, Los Angeles, Calif., a corporation of California Application May 23, 1950, Serial No. 163,769

. 26 Claims. 1

This invention relates generally to pressure control mechanisms, and relates more particular- 1y to mechanisms of this character for controlling the rate of pressure change in enclosures.

-While the invention has particular utility in connection with pressurized ventilation of aircraft cabins and the like, and is hereinafter shown and described asembodied in such a conditioning system, it is to be'understood that its utility is not limited thereto.

- It is sometimes highly desirable to produce a gradual change in the air pressure within an aircraft cabin during the flight from one altitude to another, as from a lower altitude airport to a higher one, or vice versa, and it is therefore an object of the present" invention to provide means by which the air pressure within a cabin or enclosure may be automatically changed at a predetermined rate. Thus, discomfort or harm to the occupantsof the aircraft is avoided.

It is another object of the inventionto provide mechanism of this character'which is pneumatic in'operation.

It is a further object of the invention to provide mechanism of this character, by which the pressure altitude within the cabin may be automatically andsmoothly changed at a selectably predetermined rate;

It is another object of the present invention to provide means of thischaracter whereby the pressure within an aircraft cabin may be changed at a gradual preselected rate during flight so that it will have reached a value substantially that of the ambient atmospheric pressure at the terminal airport. Thus, upon landing at an airport situated at a higher or lower altitude than at the starting point of the flight, the occupant or 00- cupants of the craft will find the atmospheric pressure at the terminal airport substantially the same as that within the aircraft when it lands at said terminal airport, thus avoiding any sudden and uncomfortable pressurechange at said airport when landing and leaving theaircraft.

"It is a further object to 'control the pressure in pressurized cabins in such manner as will permit the selection of a desired pressure within the cabin and also a desired rate of pressure change within the cabin whereby changesinpressure to which occupants of the cabin are subjected will not be so abrupt or rapid asto cause discomfort.

Let it'be supposed that an aircraft upqn leaving an airport at one altitude is to land at afield of different altitude within a'giiv en period of time. The occupants of thecabin areisubjected to pressure *kiha'nge; "produced "gradually," so that- 2 when the second landing field is reached, the pressure to which the occupants are subjected within the aircraft cabin will correspond to the atmospheric pressure at the second landing field. During the flight from the first field to the second field, although the aircraft may rise to an altitude considerably above the altitude of either landin field, the occupants of the pressurized cabin will not be conscious of this fact, but will be subjected to a reduced pressure no greater than that corresponding to the altitude of the highest of the two landing fields.

Another object of the invention is to provide mechanism of this character which will limit the rate of change in the cabin pressure.

Still another object of the invention is to provide' a device of this character that is relatively simple in construction and reliable in operation.

Other objects and advantages of the invention will appear from the following part of the specification.

Referring to the drawing, which is for illustrative purposes only,

Fig. 1 is a diagrammatic or schematic view of pressure control mechanism embodying the present invention;

Fig. 2 is a sectional view taken on line 22 of Fig. 1; and

Fig. 3 is a sectional view taken on line 3-3 of Fig. 1.

Referring more particularly to the drawing, there is shown an enclosure or cabin which is indicated generally at l 0, supplied by air under pressure by a suitable pump or supercharger II operated by any suitable source of power, not shown, for maintaining a flow of air through the cabin, for purposes of ventilation. The cabin is provided with an outlet opening l2, in a wall l3 thereof, said outlet bein controlled by an outflow valve, indicated generally at M in Fig. 1. The outflow valve M, as herein shown, constitutes a means for regulating the pressure in the cabin to a value which corresponds to the pressure selected by the control point setting mechanism which will be hereinafter described. Other types of outflow valves may be used, another example being that disclosed in the patent to Kemper No. 2,463,491.

The valve [4 will be but briefly described herein, inasmuch as a valve of this type is fully shown and described in the copending application of Arthur et al., No. 7763842, filed September 29, 19471 now Patent No. 2,531,100.

valve comprises an outwardly opening balanced valve "member I 5' in the general shape of a shallow cup, said valve member having a peripheral flange I6 having a thin or narrow edge engageable with a seat ll attached to the cabin wall and having an opening l8 which registers with the opening l2. An annular member l9, generally Z-shaped in cross section, is supported in spaced relation to the valve seat by means of,.;spa;cers:-20 through whichbolts, not shown, pass.

The member l9 includes an outwardly extending annular flange 21 referred-to bolts. The Z-shaped member-,w-also includes an annular inturned flange 22 to which one end of a flexible diaphragm -QS..isrsecured.

Th other end of the diaphragm is connected .to

the valve member ill by means of an annular collar 24. The diaphragm includes agenerally U-shaped portion 25 in the space between the member 19 and the collar 24, said U-shapedportion 25 rolling as the valve member moves axially. A generally .cup-shaped ,;cover ,26 is, attached 5130 the flange-2| and ,defines,,with the member t9, dia h a Z d va s iw aprc sure harnlo r;= 2 I.

!l? he v-alve i5 -.,is ,adapted -for axial movement andjsprDYided-with a stein-23 suitablyinounted in-,a,guide;=@9. A lightspring 5W, which vreacts between the valve member l5 and a .collar :31 on the; guide -29, ,urges the valve member iii in the closing, direction.

Mechanismfior setting the pressure in the chamber 21! is indicated generally at 3'5 and comprises ,a housing 36. .The mechanism ,35 includesa pressure ch amberalll .and a ,pressure chamber 38, thechamber 3T being-defined bya portion of .the housing 3,6 and ,a. ;uexible :diaphagm ll iwhich separates. said chambers d7 magic. ,The chamber 33, isdefinedby said ,diah agm, .3 9, and an annular =walllifl, as well as by a-Qmition, of. the hQusing 3,6.

The diaphragm 39 is a differential pressure responsive movable -.wall or. element and .ispart @of the pressure differential regulatingnmechanism for c ontrolling the. diflerence in' pressure between. the,cha1nhers '31 andf..38.

Air is bled into the chamber 38 frorna source of higher, pressure, which is shown as ,the cabin interior, but may be any source of higherv pressure air, through a restricted calibrated .ble'edJlZ, and escape of air is controlled by a valve, indicated enerally at 743.

flhe valve 43 comprises a valve cage All ,liaving abore H415 therein, for slidable,recep tion of an adjustablevalve seat 46. The ,seatflli mes centralpassage ll therein, and branch passages 42 8 terminating outwardly of a screw ll formed integrally with the seat :36. The screw extends axially of said seat and is threadably received in van ppening in an end wall 5G of the cage 14%.

Rotationof .the screw 49 effects adjustment of the seat 46, and a'lock nut 5! on saidscrew locks itinadjlusted positions. Asea152 is received in an internal groove provided therefor in thecage :lLand prevents leakage of air past thaadjvistable valve seat.

"The axial .bore in the valve seat 'has an enlai-gedportion 55 at the inner end which serves as a guide for a valve member comprising a stem 5,6,,a conical seat engagin portion 5? and an enlarged Qp0rtion58 adjacent the portionfil, said portion 58 being profiled to, provide vpassagesjlil sothatair may flow from the chamber 38 past the valve and into the upperwendsoftheporeA5, as shown in the drawing, from whencethe air may ,passto a region of .low pressure such as secured by the above 'head 84 at the lower end of the valve stem 56.

R Opposite the reenforcing plate 62 is a reenriorcing plater 65, a central region of the diaphragm 39 being clamped between said plates 62 i-and255swhich aresecured together by a rivet B5 orany other suitable well-known means.

The chamber-'SB is connected with the chamber 21,01" thewvalve slfl by means of a conduit n.

Thus, the pressure in the chamber 21 will be substantially the same as the pressure in the chamber 38, said pressure being termed the control point setting pressure ancl the ,chamber' tll being termed the l control chamber.

The chambenS'i is termed hereinzthe backeup chamberqf or purposes of convenient reference.

-5The backup-chamber "31 houses anevacuated isobaric bellows ill having ;a boss ltattone end, terminating in a screw portion 72 received in; an opening. provided therefor in the top wall of the housing 38. ;.The screw portion (iris provided with a nut i3, wherebythebellows lilsisfixedly anchored ,to said .wall adjacent the chamber tfil.

The-bellows it is .operatively :connected with the .pilot valve mechanismv bya lever .25 and a link springlfi. Morespecifically, the lever .15 has a fixedplvot 11 intermediate the ends thereof. The spring'lfiis,shownas-being generally diamond-shaped and isconnectecl ,to the ,lever, adjacent one end thereof, bya rivet l8. or,.by anyot her. suitable means, said spring ,beingconnected to the diaphragm 3.9 by meansof the rivet 56. The freeendofthebellows lll.=is,provided with .a stem i9 having a pivotal connection .39 with the lever adjacent the end thereof opposite theuspring.

The end of thellever =15 adjacentthebellows is provided with a longitudinally extending, screw 8.! having anadjustable nutBZ thereon said nut having an annular intermediate portion.rotatable within ,.,a .sleeve .83. which has ,an .ear, .84 to whichpn end of a spring isattached. The opposite end of thespring .85 is connected toa yoke 186.carrie'dby a vnutgill receive-cl onan adjustin .screw ,88, the outerend of said screw extending outwardly of the housing 38 and having an adjusting knob '89. The purpose. of the adjusting nut 82 is to change the position whereat the effective pressure of the spring 85 is exerted on the lever 75 soas to compensate for production tolerances. Movement of the .leverf'l5 is limited in both ,directions by fixed stops 9.0 and? which .are adapted to beengagedgbythe screw'llI, as will be'more particularly described hereinafter.

A rat selector valve, indicated ;at 94, has an orifice including a passage 95, in a plug 86, and later alpassages 91 and- 98 connecting said passage with the chambers ,38 ,and f3? respectively. The passage ,95 is enlarged at 99,-the enlarged part 99. of said passage extending withinavalve fixture l0 and said passage 99 is internally threaded forreception of the externallythreade'd portion ill! of an adjusting rod ,JD'Z. The threaded end. of ,the rod .1.02 ,is. provided ,with a reduced diameter, tipslfifl, slidably received in .the ar 9. n -seam d a -a i ebi re r th 5. cross passage 98, thereby adjustably restricting the fluid connection between the chamber 31 and the chamber 38. The outer end of the rod I02 extends outwardly of the housing 36 and is provided with an adjusting knob I04. .7

Operation of the mechanism Assuming that the aircraft is on the ground, the ground condition of the mechanism is as follows: Ambient atmospheric pressure exists in the chamber 38 and in chamber. .31 since it is connected to chamber 38 through the passages 98, 95. and 91. Due to the pressure in chamber 31 the evacuated bellows I is completely collapsed, and as a result the screw 8|, whichmaybeconsidered as anend portion of theleverJS, is urged against the stop 90, and when the leveris in this position the pilot valve member orpin operably connected with the diaphragm 39, is in a wide open position. At this time the chamber 38 is freely connected .with ambient atmosphere through the pilot valve and conduit 60, so that ambient atmospheric pressure exists in said chamber 38 and also in the chamber 21 of the outflow valve unit I4.

V In preparation for a flight from a lower altitude airport to ahigher altitude airport the pressure altitude selector knob 89 is adjusted to the pressure altitude of the terminal airport, or to the pressure altitude which it is desired to maintain isobarically in the cabin. .The desired rate of change of pressure altitude may also be setat this time by adjusting the rate selector knob I04 to fix the size of the orifice of the valve 94, said adjustment of the rate selector knob positioning the pinor tip I03. Under these conditions no change occurs until the airplane starts to gain altitude. When the airplane takes oif from the landing field and altitude is gained, a drop occurs in the ambient atmospheric pressure which is",;transmitted to the control chamber 38 through the open needle valve 58. Should the set rate be exceeded the pressure in the chamber 38 will drop below the pressure existing in the chamber'3'l', and a pressure differential will be set up across the orifice of the valve 94 as'well asacross the diaphragm 39. This will cause the diaphragm to move in a direction against the tension of the spring 16 to move the valve 43 "in theclosing direction. There will then be an interaction between the forces acting on the diaphragm 39 and the action of the spring I6 which will result in positioning the metering pin 51 so as to maintain a substantially constant differential pressure across the orifice of the valve 94.

Except for sudden surges there is very little movement of the parts but there is a continual application of forces between them. The differential pressure between the chamber 38 and the chamber 31 will usually remainat a substantially constant value, for example, about .5" H2O;

It will be understood that by thus continuing to maintain a substantially constant differential pressure across the orifice of the valve 94, the rate of change in pressure in the back-up chamber 31 is determined, and consequently, the rate of change in pressure in the control chamberand the pressure in the pressure chamber 21 behind the sensing valve I of the cabin outflow valve unit I4, is also determined. By gradually changing the.

pressure in the pressure chamber 21 by means of the control point setting mechanism, the cabin pressure will bechanged fromonepressure altifurther expansionof said bellows.

tude to another. The rate at which the cabin pressure will change frome one value to another is determined by the setting of the valve 94.

- As the pressure in the chamber 31 falls, it will reach a value where it is no longer high enough to exert sufiicient pressure on the evacuated bellows I0 to maintain the bellows in the collapsed position against the tension which has been set into the .isobaric spring 85.

The bellows will, therefore, expand under the influence of the spring'85 causing the end of the arm 15 to move to a position intermediate of the stops 90 and 9|. This will relax the tension of the spring I6. At this time the pressures in the chambers38 and-31 are substantially equal. However, a -difierential in pressure across the diaphragm 39 is no longer required to operate the valve 43 which is, at this time, moved toward the closed or metering position by the action of the bellows I0. Since th pressure in the chamber 38 follows that in the chamber 31, the control pointsetting remains constant-and cabin pressure will, therefore, be maintained essentially constant. The cabin pressure is maintained at the desired value, for example, at about 2.5" H20 higher than the pressure in the controlchamber 30 as determined by the pressure or-force exerted on the valve member I5 by the spring 30.

Under the conditions ofisobaric control an equilibrium condition exists-wherein there is no differential of pressure betweenthe pressures prevailing in the chambers-38 and 31 due to the balanced action of the iso'baric bellows I0 and the isobaric spring acting through the lever I5 and the valve spring I6 to re-position the'valve 51 in response to any change in the pressure in the chamber 38.

When a flight is to be made from a higher to a lower altitude airport, the altitude selector knob 89 is adjusted for the terminal airport pressure and is moved in a direction to increase the force of thespring 85 on the isobaric bellows 10, said bellows being expanded to a point whereat the screw 8| engages the stop 9|, thereby limiting The action of the device is then the reverse from that described in connection with a flight from a low altitude airport to a higher altitude airport. ,If necessary, the valve 94 is also adjustedby means of the knob I04 to provide the required rate, of pressure change.

It will be understood, of course, that the term aircraft as used herein, refers to any device adapted to pass through theearths atmosphere.

I claim:

1. In a pressure control mechanism: walls defining a control pressure chamber having an inlet passage and an outlet passage; means for controlling the pressure in said control chamber comprising a differential pressure sensitive element subjected on one sideto pressure in said control chamber and adapted to control one of said passages; a connection between the other side of said element and the control chamber, said connection including a relatively large capacity portion interposed therein; means forming a restriction between said large capacity portion of the connection and the control chamber; and an-absolute pressure responsive device subjeicted tothe same pressure assaidother side ofsaid element and adapted to cooperate with saiddifierential pressure responsive element in controlling said one-passage, I I

M ehse smr prs whiten -the Pressure in pheric pressure gfor grad ually varyingfsaid con-.

trol chamber' pressure over-a predetermined period of time, and; pressure sensitive means "subjected .to the pressure of saidregion -and cooperable with said pressure sens itivemeans in-the control of the pressure -in said-control chamber;

. 3. Mechanism for-controlling; the pressure in an enclosurecomprising pressure; contrel means operable to*-control-. the; pressure in- -said enclosure, said. pressure control I means including 1 a movable pressure sensitive elementgwallsgdefining a control pressure chamber, said. movable pressure sensitive controlaelernent being exposed on one side to control-chamber pressure-andon the other side to enclosure pressure; rneans for regulating said-control pressure,- incl-uding a pressure responsivetdevicef having .a movable wall operable ata controlled rate of; response and re sponsive to variations in'the difierential of pressure between thatin the control chamber and a regionof control pressure, said-region having a connection with the control chamber, forgradually varying said control chamber pressure over a predetermined. period, of time; 4 and means subjectedto pressureof said region 'foiyarresting control chamber .vpressure ,at .a predetermined value.

.4. Iii-pressure control mechanism: means defming a. pair o'iipressure chambers having a restricted connectiontherebetween; and means for controlling the pressure in one of saidchambers comprising pilot valve means ,includinga pressure responsive element responsive to variations in the differential of pressure .7 between said chambers forfcontrolling the flow .offiuid relativ ejto said one chamber, andpreswre responsive mean-s having one side exposedto pressure in'the other of said chambers for controlling the pressurein said one a chamber.

5. In pressure control mechanis nz gmea'ns defininga pair of pressure chambers'having ia ra stricted connection therebetween, one for said chambers being'of larger capacity thanthe other of said chambers; jan d means for controlling the pressure in the smaller of said chambers comprising pilot valve means including a'pilot valve and a pressure A responsive element controlling same, said pressure responsive element being responsive to'variations in the differential of pressure between saidchambers, and pressure responsive means, responsive, to the absolute pressure in the larger chamber and adaptedto cooperate in the control of saidpilot valve.

6.;In pressure control mechanism: means defining a pair of pressure chambers having a restricted connection therebetween, one of said c'hambers'being of larger capacity than the other; and means for controlling the pressure in one of said chambers comprising pilot valve means including a pilot valve'member'adapted to control the' now fiif fili-id relative to th' sma1lerchamber,-.ag.pressure'responsiveavelement responsive-to variations .in' the differential of: pressure; between said chambers andladapted to actuate saidgpilot valve member, and absolute pressure responsive means exposed. to the .pressure in. :the 'larger chamber andadapted to cooperate in the control of the pilot'valve member.

"I. .Thewinvention' defined by claim 6, iwherein the pressuret responsive. element and the-pressure responsivehmeans. are arranged in series.

In pressure control mechanism: meansdefiningalpair of ipressure chambers having.. a-- re strictednconnection therebetweenyand means for controlling theipressure in one of-saidchambers, comprising pilot valve means including .--a...pilot valvehaving an adjustable. seat part :"and a-movable valve :lmember, cooperating therewith tfor controll-ingthe flow of fluid relative to saiduone chamber,apressure responsive element responsivei to. variations in the differential of. pressure between said chambers andpressure responsive means having oneside exposed to: pressure in the other. of said chambers, said pressure: responsive elementand pressureresponsive means cooperating to control said pilot valve.

A 9. ;The invention defined by claimt, wherein the pressure responsive element and; pressure responsive 1114981118 are connected together with yielding resilient means.

1 0. ;The invention defined'by claimsgs, wherein a link springis interposed ,between; the pressure responsive element and the I pressure responsive means for connecting; the. same together.

11.. In pressure controlmechanism: means defining apair of pressure chambers having-garcstricted cannectiontherebetween; and means; for controlling the pressure in-one of-saidichambers, comprising pilot valve means including-a pressure responsive element responsive to variations in the differential of pressure between said chambers for'controlling the flow of-flu-id relative to saidpne chamber; absolute pressure responsive means responsive to the pressure in; the other of said chambers for -controlling the pressure in said onechamber; means; limiting the movement of said absolute pressure responsive means in both directionsbut permitting limited movement thereof, and means for adjusting the; response said pressure responsive means.

12. In pressure control mechanism: wall means defining-a control pressure chamber; means for controlling the pressure in said chamber comprising a. valve member for controlling the flow oi -fluid relative tosaid chamber psi-pressure responsiveelement for controlling said valve memher, said pressure responsive. element being ex posed ononeside topressure in said control chamberand being-exposed on the other side to a region-of variable controlled pressure urging thepressure responsive element in a direction-to efiectclosing movernent o f said valvemember; and an absolute pressure responsive device exposed to the. pressure vin said =region and operably .ccnnected with said-pressure responsivelement for cooperative .action 'in the control of said valve member.

13. The inventiondefined by claim 1-2,.Wherein expansion of said absolute pressure responsive device urges thevalvemember in the closing direction. a 14. The invention defined by claim '12, wherein there is a slavevalve unit having a, pressure chamber connected with the control pressure chamber. r

' -15. Pressure control mechanism, comprising:

wall means defining'a control pressure chamber and a back-up chamber of substantially larger capacity than the control pressure chamber; a :valve, including a movable valve member, for

controlling-the flow of fluid relative to the control chamber; passage means connecting said chambers; adjustable means for variably restricting said passage means; a differential pressure responsive element for controlling said valve member and responsive to variations in the differential of pressure between that in the control chamber and the back-up chamber; an absolute pressure responsive device responsive to the absolute pressure in the back-up'chamber; a lever pivoted intermediate its ends and having one end operably connected to the pressure responsive device; a link spring connected to the other end of the lever and connected to the differential pressure responsive element; a pair of stop members spaced apart relative to the path of movement of said lever for limiting the movement of said lever in both directions; means for loading the pressure responsive device; and adjustable means for varying said loading.

16. In pressure control mechanism: walls defining a control pressure chamber having an inlet passage and an outlet passage; means for controlling the pressure in said control chamber including a valve controlling one of said passages and a difierential pressure sensitive element subjected on one side to pressure in said control chamber and adapted to control said valve; a connection between the other side of said element and the control chamber, said connection including a relatively large capacity portion interposed therein; means forming a restriction between said large capacity portion of: the connection and the control chamber; and an absolute pressure responsive device subjected to the same pressure as said other side of said element and adapted to cooperate with said differential pressure responsive element in controlling said one passage.

1'7. In a pressure control mechanism: walls defining a control pressure chamber having an inlet passage and an outlet passage; means for controlling the pressure in said control pressure chamber comprising a differential pressure responsive device subjected on one side to pressure in said control chamber and adapted to control one of said passages; a connection between the other side of said device and the control chamber including a relatively large capacity portion and a restriction between said portion and said chamber; and an absolute pressure responsive device subjected to pressure in said connection and adapted to cooperate with the differential pressure responsive device in controlling said one passage.

18. In a pressure control mechanism: means defining a pair of pressure chambers having a connection therebetween; and means for controlling the pressure in one of said chambers comprising pilot valve means including a pressure responsive element responsive to variations in the differential of pressure between said chambers for controlling the flow of fluid relative to said one chamber, and pressure responsive means having one side exposed to pressure in the other of said chambers for controlling the pressure in said one chamber.

19. In pressure control mechanism: means defining a pair of pressure chambers having a restricted connection therebetween; and means for controlling the pressure in one of said chambers comprising pilot valve means including a pressure responsive element responsive to variations in the differential of pressure between said chambers for controlling the flow of fluid relative-to said one chamber, and pressure responsive means mechanically connected with said pressure responsive element and having one side exposed to pressure in the other of said chambers for controlling the pressure in said one chamber.

20. In pressure control mechanism: means defining a pair of pressure chambers having a restricted connection therebetween; means for controlling the pressure in one of said chambers comprising pilot valve means including a valve for controlling the fiow of fluid relative to one of said chambers; a pressure responsive element responsive to variations in the differential of pressure between said chambers for controlling said valve; and pressure responsive means having one side exposed to pressure in the other of said chambers and cooperable with the pressure responsive element in the control of said valve.

21. In pressure control mechanism: a first chamber; a second chamber; movable wall means subject on opposite sides to the pressures in said chambers, means for controlling the pressure in said first chamber, said means being operated by said movable wall means; pressure'responsive means in said second chamber; means connecting said pressure responsive means to said movable wall means; and means connecting said chambers together.

22. In pressure control mechanism: a first chamber; a second chamber; movable wall means subject on opposite sides to the pressures in said chambers, means for controlling the pressure in said first chamber, said means being operated by said movable wall means; absolute pressure responsive means in said second chamber; means connecting said pressure responsive means to said movable wall means; and means connecting said chambers together.

23. In pressure control mechanism: means defining a pair of pressure chambers having a restricted connection therebetween; and means for controlling the pressure in one of said chambers, comprising pilot valve means including a pressure responsive element responsive to variations in the differential of pressure between said chambers for controlling the flow of fluid relative to said one chamber, pressure responsive means having one side exposed to pressure in one of said chambers, and means connecting said pressure responsive means and pressure responsive element in series with respect to each other.

24. In pressure control mechanism: means defining a pair of pressure chambers; means forming a connection between said chambers; means for adjustably restricting said connection; and means for controlling the pressure in one of said chambers, comprising pilot valve means including a, pressure responsive element responsive to variations in the difierential of pressure between said chambers for controlling the fiow of fiuid relative to said one chamber, pressure responsive means having one side exposed to pressure in one of said chambers for controlling the pressure in said one chamber, and means connecting said pressure responsive means and pressure responsive element in series.

25. In pressure control mechanism: means defining a pair of pressure chambers having a restricted connection therebetween; and means for controlling the pressure in one of said chambers, comprising pilot valve means including a pressure responsive element responsive Fto variations in the differential of pressure betweerl'said chamhers for controlling thefiow of "fluid relativeto said one chamben pressure responsive meanshaving one side exposed to pressureinone of said chambers; and resilient meansconnectingsaid pressure responsive means and pressureresponsive element in series With respect to each other.

26. In pressure control mechanism: a first chamber; a second chamber; movable Wall means 12 said chambers; resilient meansico'nnectingsaid pressure responsive meansandsaid movable wall means for cooperative controlof the means for controlling the'pressure in said 'first chamber; and means connecting said chambers together; RICHARD A. FISCHER;

References Cited .in the file of this patent UNITED STATES PATENTS Number Name Date r 2,463,487 Widgery et a1. ,Mar.',1,. 1949 2,513,332 Kemper July 4, 1950 2,531,100 Arthur et al Nov. 21, 1950 

